float PHBeckmann( float ndoth, float m ) {
    float alpha = acos( ndoth );
    float ta = tan( alpha );
    float val = 1.0 / ( m * m * pow( ndoth, 4.0 ) ) * exp( -( ta * ta ) / ( m * m ) );
    return val;
}
float KSTextureCompute( vec2 tex ) {
    return 0.5 * pow( PHBeckmann( tex.x, tex.y ), 0.1 );
}
void main() {
    float x = KSTextureCompute( iTexCoords );
    oColor = vec4( x, x, x, 1.0f );
}